This invention relates to a magnetic recording medium in which a magnetic layer is formed by coating on a non-magnetic base material a magnetic paint containing a magnetic powder and a binder as its main components. More specifically, this invention relates to a magnetic recording medium having high dispersibility of the magnetic powder and improved abrasion resistance and flexibility of the magnetic layer.
Recently, despite advances in the field of magnetic recording media, there is in particular, a strong demand for both high-density recording and short wave-length recording and also for improved strength of the magnetic layer. To achieve these recording goals, it is necessary to improve the degree of filling of the magnetic powder, i.e., the dispersibility of the magnetic powder. On the other hand, the improved strength of the magnetic layer is dependent on the kind of resin used as the binder.
There have been proposed a wide variety of binders with a view to improving the dispersibility of the magnetic material and the strength of the magnetic layer. For example, compositions comprising a thermosetting resin such as phenolic resin, epoxy resin and melamine resin or a thermoplastic resin such as polyvinyl butyral have heretofore been proposed. When a thermosetting resin such as a phenolic resin is used as the binder, the dispersibility and the abrasion resistance are likely to be improved. However, phenolic resins are still inadequate in that they are generally low in molecular weight; are unavoidably admixed with low molecular weight components which are partially responsible for the generation of drop-out in recording play-back; are inferior in flexibility after curing; and are almost insoluble in solvents of low polarity which are widely used in magnetic paints.